The present invention relates to a polyester laminated film obtained by extrusion-laminating an ethylene copolymer resin onto a polyester film, exhibiting excellent interlayer adhesiveness to the polyester surface, and to a method of producing the same. More specifically, the invention relates to a method of producing a polyester laminated film having excellent interlayer adhesiveness by the extrusion-lamination without effecting the anchor-coat treatment on the polyester film or without effecting the ozone treatment on the laminated resin film, and to a laminated film obtained by the above method.
A polyester film and, particularly, a biaxially stretched polyester film exhibits excellent transparency, toughness and oxygen barrier property, and has been widely used as a base member of packaging materials for packaging foods and industrial materials. In practice, other base member that plays the roll of a reinforcing member, such as polyamide film, ethylene/vinyl alcohol copolymer, aluminum foil, aluminum-deposited polyester film, inorganic material-deposited polyester film or paper, is further laminated on the polyester film and, besides, a heat-sealing resin layer is laminated thereon to impart heat-sealing property.
The films can be laminated by such a laminating method as dry-laminating method, wet-laminating method or extrusion-laminating method. Among them, the extrusion-laminating method is widely used which is most advantageous from the standpoint of cost of production and efficiency. Here, the lamination of the polyester film on the other base member, or the lamination of a heat-sealing layer on the polyester film, is executed by a method which extrusion-laminates an adhesive resin between the polyester film and the other member for the former case or is executed by a method which extrusion-laminates a heat-sealing resin on the polyester film for the latter case.
Here, in order to reinforce the interlayer adhesion between the polyester film and the laminated resin, there is generally employed either (1) a method of effecting the extrusion-lamination after the anchor-coating agent has been applied onto the surface of the polyester film, or (2) a method of executing the ozone treatment on the surface of the molten resin film on where the extrusion laminate is to be adhered as well as the corona treatment and flame treatment on the surface of the polyester film at the time of executing the extrusion lamination. Otherwise, so high interlayer adhesion is not obtained.
However, the above-mentioned method (1) involves such problems as deteriorated working environment due to the scattering of a diluting organic solvent such as ethyl acetate or toluene used as the anchor-coating agent at the time of extrusion-lamination, a rise in the cost of production due to the use of a relatively expensive anchor-coating agent and offensive odor due to organic solvent remaining in the final product (packaging material). On the other hand, the above-mentioned method (2) involves such problems that expensive ozone-treating apparatus and surface-oxidizing apparatus must be provided in a process in the extrusion-laminate processing, requiring extra investment for the facilities and driving up the cost of operation.
It has therefore been strongly urged in the field of packaging industries to provide a method of producing a polyester laminated film having favorable interlayer adhesiveness by the extrusion-laminating method without using the anchor-coating agent or the ozone-treating apparatus which has been so far considered essential. In order to satisfy the above requirement, therefore, the present inventors have conducted keen study, have discovered the fact that use of the anchor-coating agent and the ozone-treating apparatus can be omitted when a resin having a particular composition is extrusion-laminated on the polyester film, and have arrived at the present invention.
It is therefore an object of the present invention to provide a method of producing a laminated film having excellent interlayer adhesiveness based on the extrusion-lamination method by laminating the polyester films or by laminating the polyester film on another base member film, and a laminated film obtained by this method.
That is, the present invention is concerned with a laminated film obtained by extrusion-laminating, onto at least one surface of a polyester film, an ethylene/unsaturated carboxylic acid/(meth)acrylic acid ester copolymer or a mixture resin composition thereof with an ethylene/unsaturated carboxylic acid copolymer and/or an ethylene/(meth)acrylic acid ester copolymer, the amount of the unsaturated carboxylic acid component being from 1 to 12% by weight and the amount of the (meth)acrylic acid ester component being from 2 to 25% by weight with respect to the total amount of said extrusion-laminated resin components.
The invention is further concerned with a laminated film obtained by extrusion-laminating, onto at least one surface of a polyester film, a mixture resin comprising:
(a) 100 parts by weight of the mixture resin component of an ethylene/unsaturated carboxylic acid/(meth)acrylic acid ester copolymer or the mixture resin composition of said ethylene/unsaturated carboxylic acid/(meth)acrylic acid ester copolymer with an ethylene/unsaturated carboxylic acid copolymer and/or an ethylene/(meth)acrylic acid ester copolymer, the amount of the unsaturated carboxylic acid component being from 1 to 12% by weight and the amount of the (meth)acrylic acid ester component being rom 2 to 25% by weight with respect to the total amount of the extrusion-laminated resin components, and
(b) not more than 30 parts by weight of an ethylene/xcex1-olefin copolymer resin having a density of 840 to 900 kg/cm3.
The invention further relates to a method of producing the laminated film by extrusion-laminating, at a resin temperature of 280 to 340xc2x0 C., the above extrusion-laminate resin onto a polyester of which the surface has been oxidized and having a surface wet tension of not smaller than 45 dyns/cm.